Mechanism behind information leakage in electromagnetic analysis of cryptographic modules

This paper presents radiation mechanism behind Electromagnetic Analysis (EMA) from remote locations. It has been widely known that electromagnetic radiation from a cryptographic chip could be exploited to conduct side-channel attacks, yet the mechanism behind the radiation has not been intensively studied. In this paper, the mechanism is explained from the view point of Electromagnetic Compatibility (EMC): electric fluctuation released from a cryptographic chip can conduct to peripheral circuits based on ground bounce, resulting in radiation. We demonstrate the consequence of the mechanism through experiments. For this purpose, Simple Electromagnetic Analysis (SEMA) and Differential Electromagnetic Analysis (DEMA) are conducted on FPGA implementations of RSA and AES, respectively. In the experiments, radiation from power and communication cables attached to the FPGA platform is measured. The result indicates, the information leakage can extend beyond security boundaries through such cables, even if the module implements countermeasures against invasive attacks to deny access at its boundary. We conclude that the proposed mechanism can be used to predict circuit components that cause information leakage. We also discuss advanced attacks and noise suppression technologies as countermeasures.